Priming of stomatal precursors by SPEECHLESS enables modulation of stomatal development by long-distance drought signals

Xin Yang, On Sun Lau
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117557.

Stomata, the epidermal pores of plants, play a crucial role in gas exchange by taking in carbon dioxide and releasing oxygen and water vapor. Previous studies have shown that plants can adjust stomatal production to adapt to varying environmental conditions. We previously demonstrated that under drought, the phytohormone abscisic acid (ABA) activates a sub-family of the SNF1-related protein kinases, SnRK2s, in meristemoids to phosphorylate and down-regulate the master regulator of stomatal development, SPEECHLESS (SPCH), leading to reduced stomatal formation. However, how ABA levels in the stomatal precursors cell is regulated by drought remains unclear. Here, we report an osmotic stress-induced root-to-shoot systematic regulation of stomatal development that is enabled by SPCH. SPCH drives the expression of members of the receptor-like kinases (RLKs) BARELY ANY MERISTEM (BAM) family in meristemoids. During water stress, the root-to-shoot mobile peptide CLE25 is induced and is perceived by the BAM receptors. This activates the expression of ABA biosynthetic enzyme gene in meristemoids, leading to accumulation of ABA within and suppression of stomatal development. Thus, the induction of BAM by SPCH primes the stomatal lineage cells to perceive drought signals, revealing a mechanism by which plants can confer responsiveness to environmental stimuli in a cell-type-specific manner.